The prior art of generating tunable vacuum ultraviolet radiation by means of a four-photon mixing process (R. T. Hodgson et al, Physical Review Letters, 32, 343 (1974)) had known that for a conversion medium such as Strontium vapor, the atoms of which have two electrons in their outermost shells, the output power is increased when the output frequency is near the frequency of an autoionizing state.
Shifting the frequency of an excited state or broadening the resonance by means of the Stark effect had been known in other contexts, such as tuning molecular energy levels (R. L. Abrams et al, IEEE Journal of Quantum Electronics, QE-13, 82 (1977)), but one skilled in the art would have assumed that it was not possible to shift autoionizing states by means of the Stark effect.